This invention relates to data communications over electrical distribution systems, and more particularly, to a method for maintaining a constant root mean square (rms) current level on a communications channel by controlling the firing of a power control electronic component.
Data communications over an electrical distribution system to ascertain performance at various locations throughout the system are well-known in the art. Communications can be in either an outbound direction; i.e., from a central location to outlying locations, or inbound; i.e., information transmitted from the outlying locations back to the central location. Various features and requirements of such a system are disclosed and described in U.S. Pat. Nos. 5,486,805; 5,198,796; 5,262,755; 4,996,513; 4,963,853, 4,918,422; 4,914,418; and 4,658,238. All of these patents are assigned to the same assignee as the current application.
For inbound communications from a remote to a central site, a minimum current level (peak or rms) must be available at the input to a transponder in order for the incoming data to be properly received and processed. Because the carrier wave has a generally sinusoidal waveform, it is the common practice to sense a data signal riding on the carrier at a point approximately 30.degree. before zero crossing of the waveform. In designing the transponder, the components employed must be capable of tolerating the current levels associated with the signal.
There are several problems with the present inbound signaling technology, the biggest of which is cost. Present inbound components cost more than a quarter of the total cost of a product such as a SMT (surface mounted transformer) or an IMT (impedance matching transformer). One reason for this high cost is the inductor used in the unit must be capable of dissipating very high power levels; e.g., up to 500 watts. The inductor must also operate over a very wide range of voltages and over a wide range of power ratings for the power transformer into which the signal is directed. The transformer range is from 15 KVA, up to 500 KVA. Accordingly, the inductor must be designed so a sufficient TWACS inbound signal is generated when a 15 KVA transformer is used; and, the inductor must not overheat if a 500 KVA transformer is the signal source. If means were available by which the strength of the inbound current pulse could be measured, so adjustments could then be made to maintain a fixed current level, then an inductor not requiring a lot of excess capacity could be used. This would mean a lower cost component, and more capacity in a firing circuit if the present element is used.
In designing new products, the ability to operate at several different voltages would also be highly desirable. Operating voltages include, for example, 120v, 208v, 240v, 277v, 480v, and 600v. An inbound circuit operating over part or all of this range of voltages further reduces costs because the higher volume of use would decrease per unit cost. Further, there are meters currently available which are capable of multi-voltage operation and so could be used for part, or all, of the operating voltages. By providing the capability to adjust the firing angle at which the inbound signal is triggered, a point can be selected at which the maximum RMS current is substantially lower than has been heretofore possible. A current having a 10-15 amp value, for example, is reasonable to expect, whereas before a 30 or 40 amp value would be needed. As noted, providing such a capability would result in more flexible operation and create substantial cost savings.